Hot press insulating system



Aug. 19, 1969 H. E. MCMILLEN 3.461,!09

HOT I PRESS INSULATING SYSTEM Filed June 2, 1967 5 Sheets-Sheet l FIG.1.

4 /50 I30. A I06 lNl/ENTOR HARRY E. MCM/LLEN Aug. 19, 1969 H. E.MCMILLEN HOT PRESS INSULATING SYSTEM 5 Sheets-Sheet 2 Filed June 2. 19675 mi m; VMW WW4 HAZE/5, Mean, RUSSELL & KER/v 8- 19, 1959 H. E. MCMILLEN3,461,709

HOT PRESS INSULATING SYSTEM Filed June 2, 1967 5 Sheets-Sheet 5 HARRY 5.Ma M/LLE/V 5y 11/5 ATTORNEYS HARP/5, Macy, Russzu 6% KERN Aug. 19, 1969I H. E. MCMILLEN now PRESS INSULATING SYSTEM Filed June 2, 1967 5Sheets-Sheet 4 7 f INVEAJTOR 64 HARRY E MCM/LLEA/ 5y H/S ATTORNEYSHAE'Q/57 K/EcH, R0555 & Ksezv United States Patent 3,461,709 HOT PRESSINSULATING SYSTEM Harry E. McMillen, Rolling Hills, Calif., assignor toMurdock, Inc., Compton, Calif., a corporation of California Filed June2, 1967, Ser. No. 643,100 Int. Cl. B21d 37/16 U.S. Cl. 72-342 13 ClaimsABSTRACT OF THE DISCLOSURE An insulating system for the heatedinterplaten working zone of a hot press comprising: heat shieldsrespectively extending along the open sides of the working zone;refractory layers engaging the surfaces of the platens opposite theworking surfaces thereof; and insulating members respectively extendingalong the edges of the platens. Some of the heat shields are movable toinoperative positions to permit access to the working zone. Eachrefractory layer comprises a plurality of separate refractory blocksbolted to the corresponding platen in such a way as to permit relativeexpansion and contraction of the platen and the refractory blocks.

Background of invention The present invention relates in general to ahot forming or sizing and stress relieving press and, more particularly,to a hydraulic press having heated upper and lower platens definingtherebetween a heated working zone in which forming or sizing and stressrelieving operations may be performed utilizing suitable dies mounted onthe platens. The invention is particularly applicable to a hot press forforming or sizing and stress relieving parts made of metals, such astitanium, requiring high temperatures, e.g., temperatures ranging ashigh as 2000 F. or more.

Operating temperatures of the foregoing magnitude within the workingzone have created numerous problems in prior hot presses for performingforming or sizing and stress relieving operations of the nature inquestion. For example, excessive heat losses from the working zone havebeen a severe problem, both from the standpoint of reduced operatingefficiency of the machine and from the standpoint of the comfort andsafety of the operator or operators thereof. Considering anotherproblem, prior hot presses of the type under discussion are providedwith large refractory layers behind the platens, i.e., above the upperplaten and below the lower platen, to reduce heat losses from theworking zone and to protect other components of the machine fromexcessive heat. Cracking of such large refractory layers due todifferential thermal expansion and contraction of the refractory layersand the platens has been a serious problem. Furthermore, such largerefractory layers are difficult and expensive to replace when crackingor decomposing occurs.

Summary and objects of invention With the foregoing as background, ageneral object of the invention is to provide a hot forming or sizingand stress relieving press which eliminates problems such as thosehereinbefore discussed.

More particularly, a primary object of the invention is to minimize heatlosses from the open sides of the interplaten working zone through theuse of peripheral heat insulating means extending around the sides ofand enclosing the working zone. A related object is to provide aperipheral heat insulating means comprising heat shields which extendalong the respective sides of the Working zone and at least some ofwhich are retractable into inoperative positions to provide for accessto the working 3,461,709 Patented Aug. 19, 1969 zone. Such heat shields,in conjunction with other heat insulation to be discussed, render the:working zone, in effect, an enclosed furnace for more efficientoperation and for greater comfort and safety for personnel.

Another object in the foregoing connection is to pivotally suspendcertain of the retractable heat shields on arms extending radially fromshafts adapted to be pivoted through predetermined angles to move thecorresponding heat shields between their operative and inoperative orretracted positions.

Still another object of the invention is to provide a hot press havingplaten-edge insulating means respectively extending along the edges ofthe platens for minimizing heat losses by radiation from the platenedges.

An important object of the invention is to provide a platen-refractoryassembly wherein the refractory layer behind the platen comprises aplurality of separate refractory blocks connected to the platen in sucha manner as to permit relative thermal expansion and contraction of theplaten and the refractory blocks while permitting removal andreplacement of individual blocks whenever required because of cracking,decomposing, or the like. With this construction, whenever a portion ofthe refractory layer is defective for any reason, the situation can beremedied readily by simply replacing the corresponding refractory blockor blocks, instead of a single, large refractory layer. Not only is itless expensive to replace a single block, or a limited number of blocks,but such relatively small blocks are much easier to handle, in removingand installing them, than a single, large refractory layer.

Another object is to connect the refractory blocks to the platen bymeans of bolts disposed in openings in either the blocks or the platen,and preferably in the latter, which are laterally enlarged substantiallyalong lines radiating from the center of the platen. With thisconstruction, the platen can expand and contract, relative to therefractory blocks, along lines radiating from the center of the platen,as the platen temperature increases and decreases, without imposingundue stresses on the refractory blocks. Whenever replacement of aparticular refractory block, or a limited number of such blocks, isnecessary, this can be accomplished readily by unbolting same andsubstituting a replacement or replacements.

Still another object of the invention is to provide a platen assemblycomprising compression springs encircling the bolts mentioned foryieldably biasing the platen and the refractory blocks together.

The hereinbefore outlined combination of peripheral heat insulatingmeans along the open sides of the working zone, platen-edge insulatingmeans extending along the edges of the platens, and individuallyreplaceable refractory blocks behind the platens, creates within theheated interplaten working zone a furnace-like environment havingminimum heat losses. Not only does this make for more eflicientoperation of the hot press of the invention, but it greatly increasesthe safety and comfort of personnel operating same, which are importantfeatures of the invention.

The foregoing objects, advantages, features and results of the presentinvention, together with various other objects, advantages, features andresults thereof which will be apparent to those skilled in the hot pressart in the light of this disclosure, may be achieved with the exemplaryembodiment of the invention described in detail hereinafter andillustrated in the accompanying drawings.

Description of drawings In the drawings:

FIG. 1 is an elevational view of a hot forming or sizing and stressrelieving press which embodies the invention;

FIG. 2 is a view, partially in section and partially in 3 elevation,taken as indicated by the arrowed line 22 of FIG. 1;

FIG. 3 is an enlarged, fragmentary elevational view taken as indicatedby the arrowed line 33 of FIG. 1;

FIG. 4 is an enlarged sectional view taken as indicated by the arrowedline 4-4 of FIG. 3;

FIGS. 5 and 6 are enlarged views respectively taken as indicated by thearrowed lines 55 and 6-6 of FIG. 2 and respectively taken as indicatedby the arrowed lines 5-5 and 66 of FIG. 7;

FIG. 7 is an enlarged, fragmentary sectional view taken as indicated bythe arrowed line 77 of FIG. 6;

FIG. 8 is a fragmentary elevational view taken as indicated by thearrowed line 8--8 of FIG. 5;

FIG. 9 is an enlarged, fragmentary sectional view taken as indicated bythe arrowed line 9-9 of FIG. 2;

FIGS. 10 and 11 are enlarged views respectively taken as indicated bythe arrowed lines 1010 and 1111 of FIG. 2 and respectively taken asindicated by the arrowed lines 10-10 and 1111 of FIG. 12;

FIG. 12 is an enlarged, fragmentary sectional view taken as indicated bythe arrowed line 12-12 of FIG. 11; and

FIG. 13 is a fragmentary elevational view taken as indicated by thearrowed line 13-13 of FIG. 10.

Detailed description of invention Referring initially to FIGS. 1 and 2of the drawings, the hot forming or sizing and stress relieving press ofthe invention is designated generally by the numeral and, in theparticular construction illustrated, includes a C-frame 22 the upper andlower arms of which respectively carry upper and lower platen assemblies24 and 26 defining therebetween a heated interplaten working zone 28. Asis conventional, the upper platen assembly 24 is vertically movable bymeans of a hydraulic cylinder 30 to open and close the hot press 20.

The lower platen assembly 26 is horizontally movable inwardly andoutwardly, between a retracted, operative position, shown in FIG. 2, andan extended, inoperative position, not shown, by means of a hydrauliccylinder 32. When the lower platen assembly is in its retractedposition, it rests on pads 34 on the lower arm of the C-frame 22, suchpads resisting the downward force applied to the lower platen assemblyby the hydraulic cylinder 30 when the press 20 is closed. The lowerplaten assembly 26 runs inwardly and outwardly between its extended andretracted positions on fixed and vertically movable rollers 36 and 38carried by the lower arm of the Gimme 22. The vertically movable rollers38 are mounted on eccentrics 40 which are pivotable to move theserollers upwardly into engagement with the lower platen assembly 26 tolift it clear of the pads 34 when it is desired to run the lower platenassembly in or out. The eccentrics 40 are operated by a hydrauliccylinder 42 through a suitable interconnecting linkage 44. The reasonfor making the lower platen assembly 26 movable outwardly or forwardlyinto an extended position is to facilitate mounting tooling, i.e., a dieor dies, on the lower platen assembly.

The upper and lower platen assemblies 24 and 26 respectively includeupper and lower platens 46 and 48 having working surfaces 50 and 52which are suitably machined to accommodate the desired dies. Forexample, the working surface 50 of the upper platen 46 is provided withmachine T -slots 54, FIG. 10, for mounting on the upper platen a die ordies matching a die or dies on the lower platen when mating dies arerequired. The working surface 52 of the lower platen 48 is provided withkeyways 56, FIG. 5, in which the desired lower die or dies may bemounted to assure positive alignment of mating dies carried by the upperand lower platens.

In addition to being capable of forming or sizing vertically, the hotpress 20 is also capable of forming or sizing horizontally by means ofsuitable mating dies movable along the keyways 56. The necessaryhorizontal forming forces are developed with a clamping action whichwill now be described in connection with FIGS. 1 and 2 of the drawings.

As best shown in FIG. 2, the lower platen assembly 26 carries aplurality of, e.g., four, pairs of horizontally spaced clamps 58 and 60respectively engageable with mating dies guided by the keyways 56. Theclamps 60 are individually actuated by horizontal hydraulic cylinders 62carried by the lower platen assembly 26 so that different formingpressures can be applied to different sets of dies simultaneously. Theclamps 58 and 60 of each pair are independently vertically adjustablefor proper alignment with the dies of the set disposed therebetween. Toachieve this, the horizontal clamps 58 are carried by and areindependently vertically adjustable by vertical hydraulic cylinders 64mounted on the lower platen assembly 26. Correspondingly, the horizontalhydraulic cylinders 62 for actuating the horizontal clamps 60 arecarried by and are independently vertically adjustable by means ofvertical hydraulic cylinders 66 carried by the lower platen assembly.With this arrangement, as will be apparent, the vertical positions ofthe various horizontal clamps 58 and 60 may be adjusted independently asrequired for proper alignment with the respective dies of the set orsets in use at any particular time.

The upper and lower platens 46 and 48 are preferably electrically heatedby means of resistance heating elements 68 and 70, respectively shown inFIGS. 12 and 7, disposed in transverse bores 72 and 74 extending throughthe respective platens 46 and 48 in parallelism with the respectiveworking surfaces 50 and 52 thereof. As respectively shown in FIGS. 13and 8, the bores 72 and 74 for the respective heating elements 68 and 70are uniformly spaced apart except in areas where bolts to be describedhereinafter are required.

As shown in FIG. 1, the upper and lower platen assemblies 24 and 26include ducts 76 and 78 respectively extending along corresponding edgesof the platens 46 and 48. The heating elements 68 and 70 are providedwith terminals, not shown, respectively located in the ducts 76 and 78.In operation, air is constantly circulated through the ducts 76 and 78as protection against burning out of the heating elements.

With the foregoing general description of the hot press 20 asbackground, the insulating system of the invention for minimizing heatlosses from the heated interplaten working zone 28 will now bedescribed. For convenience, the refractory layers behind the upper andlower platens 46 and 48 will be considered first. Thereafter, theinsulating means for the platen edges and for the open sides of theworking zone 28 will be described.

Turning to FIGS. 5 to 7 of the drawings, the lower platen 48 is shown asformed in two symmetrical halves 80, FIG. 5, seated on a refractorylayer 82, FIG. 6, formed of a plurality, shown as nine, separaterefractory blocks 84 slightly spaced apart. With the particulararrangement of refractory blocks 84 illustrated, the middle row ofblocks is common to both lower-platen halves 80.

As shown in FIG. 7, the refractory blocks 84 rest on a base plate 86forming part of the lower platen assembly 26, and are secured to thebase plate by bolts 88. In the particular construction lilustrated,there is one bolt 88 for each refractory block 84 and it is located atthe center of such block.

The lower-platen halves and the refractory blocks 84 are interconnectedin,a manner permitting relative expansion and contraction of the platenhalves and the refractory blocks in directions parallel to thelower-platen working surface 52. Also, accommodations for relativeexpansion and contraction in directions perpendicular to the workingsurface 52 are provided.

Considering how the foregoing is accomplished, bolts 90 having theirheads recessed into countersunk openings 92 in the lower-platen halves80 extend downwardly through such platen'halves and through therefractory blocks 84 and the base plate 86. Lock nuts 94 are threaded onthe lower ends of the bolts 90 and support washers 96 which serve asseats for compression coil springs 98 encircling the lower ends of thebolts 90 and bearing against the lower side of the base plate 86. Withthis construction, the springs 98 bias the lower-platen halves 80downwardly against the refractory blocks 84, and, at the same time, theypermit upward expansion due to heatmg.

As will be clear from FIGS. 5 and 6, there are two of the bolts 90through each refractory block 84. One bolt 90 of the pair of boltsextending through each refractory block 84 in the middle row extendsthrough one of the lower-platen halves 80, and the other extends throughthe other lower-platen half.

As will be clear from FIG. 5 of the drawings, the openings 92 in eachlower-platen half 80 for the corresponding bolts 90 are laterallyenlarged substantially along lines radiating from the center of thecorresponding lower-platen half. (One bolt 90 through each lower-platenhalf 80 is located at the center thereof. As shown in FIG. 5, thecorresponding bolt opening 92 is not laterally enlarged.) With thisconstruction, the lower-platen halves 80 can expand and contract alongsubstantially radial lines parallel to the lower-platen working surface52, such expansion and contraction being relative to the refractoryblocks 84.

As will be apparent from the foregoing discussion, transmission ofstresses resulting from expansion and contraction of the lower-platenhalves 80 to the refractory blocks 84 is minimized to minimize anypossibility of cracking the refractory blocks. In the event thatcracking of a particular refractory block does occur for any reason, orin the event of decomposition of a particular refractory block due tothe effects of heat after prolonged use, such a block can be replacedreadily, after removing the lowerplaten halves 80, without any necessityfor replacing any refractory blocks in satisfactory condition. This isnot true of prior single-piece refractory layers.

Referring to FIGS. to 12 of the drawings, the upper platen assembly 24has a construction which is essentially the same as that just describedin connection with the lower platen assembly 26. Consequently, it willbe discussed only briefly. The upper platen 46 is formed in twosymmetrical halves 100 seated against a refractory layer 102 composed ofclosely-spaced refractory blocks 104 suspended from a base plate 106 bybolts 108. Longer bolts 110 having their heads recessed into countersunkopenings 112 in the upper-platen halves 102 extend upwardly through therefractory blocks 104 and the base plate 106 and have lock nuts 114threaded onto their upper ends. The upper-platen halves 100 are biasedupwardly against the refractory blocks 104 by compression coil springs118 seated against the upper surface of the base plate 106 and againstwashers 116 in engagement with the lock nuts 114. The openings 112 ineach upperplaten half 100 are laterally enlarged substantially alonglines radiating from the center of such platen half. This permitsunrestricted radial expansion and contraction of each platen half 100relative to its center to minimize stress transmission to the refractoryblocks 104. (In this case, there is no bolt 110 at the exact center ofeach upper-platen half 100. Consequently, all of the bolt openings 112are laterally enlarged.)

As previously pointed out, the heat insulating system of the inventionincludes platen-edge heat insulating members respectively extendingalong the outer edges of the upper and lower platens 46 and 48 tominimize heat losses by radiation from the platen edges. (Exceptions arethe platen edges covered by the ducts 76 and 78, which themselves act asplaten-edge heat insulating members.) One such platen-edge heatinsulating member is shown in FIG. 9 of the drawings in conjunction witha corresponding edge of the lower platen 48 and is designated generallyby the numeral 120. It will be noted that the insulating member 120covers not only the corresponding edge of the lower platen 48, but alsocovers the corresponding edges of the refractory layer 82 and the baseplate 86. The insulating member 120 is removably secured in place in anysuitable manner, not shown, and may be of any suitable construction. Itis shown as comprising a fibrous heat insulating material 122 confinedin a suitable housing 124.

Turning now to a consideration of the previouslymentioned peripheralheat insulating means for minimizing heat losses from the open sides ofthe heated platen Working zone 28, such means comprises, as best shownin FIGS. 1 and 2 of the drawings, a rear heat shield 126 for the rear ofthe working zone, a front heat shield 128 for the front thereof, andside heat shields 130 for the sides thereof.

In the particular construction illustrated, the rear heat shield 126 ismade in four sections each carried by a frame 132 movable upwardly anddownwardly with one of the horizontal clamp cylinders 62. (The frames132 also carry rearwardly-extending horizontal heat shields 134 abovethe respective horizontal clamping cylinders 62 and vertical hydrauliccylinders 66 to protect same from heat from the upper platen 46 when thelower platen assembly 26 is moved forwardly into its extended positionfor a tool change.) As will be apparent, when the press 20 is closed,the rear heat shield 126 is in close proximity to the rear edges of theupper and lower platens 46 and 48 to minimize heat losses from the rearside of the interplaten working zone 28.

Similarly, when the press 20 is closed, the front and side heat shields128 and 130 are located in close proximity to the front and side edgesof the upper and lower platens 46 and 48 to minimize heat losses fromthe front and sides of the interplaten working zone 28. These heatshields are movable upwardly from their operative, heat insulating,positions into inoperative, retracted positions for access to the lowerplaten 48 and/ or the working zone 28 in general. More particularly, thefront heat shield 128 is movable upwardly into its retracted position toclear any die or dies on the lower platen 48 when the lower platenassembly 26 is rolled forwardly for a tool change. The sideheat shields130 are movable upwardly into their retracted positions for access tothe interplaten working zone 28' to permit insertion of a part or partsto be formed or sized and stress relieved, and to permit removal of suchparts after the desired operation has been completed.

The front heat shield 128 is suspended from cables 136 which are trainedaround pulleys 138 140 and 142 on the upper arm of the C-frame 22 andwhich have counterweights 144 attached to their ends. Whenever it isdesired to roll the lower platen assembly 26 forwardly, thecounterweighted front heat shield 1258 is elevated into its retractedposition in any suitable manner, not shown. If desired, a suitableactuating means, not shown, may be provided for this purpose.

Each side heat shield 130 is provided at its upper edge with upstandingbrackets 146 connected by pivots 148 to arms 150 carried by andextending radially from a pivotable shaft 152 parallel to thecorresponding side heat shield and mounted in bearings 154 on the upperplaten assembly 24. With this construction, each side heat shield 130 ispivotally suspended from the corresponding arms 150. As shown in FIG. 1of the drawings, by pivoting the shafts 152 in directions and throughangles such that the arms 150 are swung from downwardly-extendingvertical positions into upwardly-andoutwardly extending positions, thecorresponding side heat shields 130 are moved upwardly and outwardlyfrom their operative positions to their retracted positions, remainingvertical as this occurs due to the pivotally suspended mountings thereofon the arms 150. Preferably,

suitable stops 156 engageable by the arms 150 are provided to limit theretracted positions of the side heat shields 130'.

The shafts 152 may be pivoted in various ways to displace the side heatshields 130 between their operative and retracted positions. As bestshown in FIG. 3, the actuating means for each shaft 152 preferablycomprises a double-acting hydraulic cylinder 158 the piston rod of whichis connected to the corresponding shaft 152 by suitable gearing, notshown, within a gear box 160.

Each of the side heat shields 130 preferably has the construction shownin cross section in FIG. 4 of the drawings. Referring thereto, the heatshield 130 shown includes an angle-section frame 162 defining the edgesof the shield and the periphery of the external surface thereof. Theinternal surface is defined by a screen 164 secured to the frame 162, asby bolts 166. Between the internal and external surfaces of the heatshield 130 are an inner layer N8 of fibrous insulation and an outerlayer 170 of insulating board. Examples of suitable materials for theinner and outer layers 168 and 170 are Kaowool and Marinite,respectively.

With such insulating materials for the inner and outer layers 168 and170, the temperature within the heated working zone 28 may be of theorder of 2000 F., yet the outer surfaces of the heat shields 130 arecool enough to touch. The rear and front heat shields 126 and 128 mayhave similar constructions.

Although an exemplary embodiment of the invention has been disclosedherein for purposes of illustration, it will be understood that variouschanges, modifications and substitutions may be incorporated in suchembodiment without departing from the spirit of the invention as definedby the claims which follow.

I claim as my invention:

1. In a hot press, the combination of (a) upper and lower platenassemblies respectively including upper and lower platens, said upperplaten assembly being movable upwardly and downwardly away from andtoward said lower platen assembly;

(b) means for heating at least one of said platens to provide a heatedworking zone therebetween;

(c) peripheral heat insulating means extending around the sides of andenclosing said working zone for minimizing heat loss therefrom;

((1) said peripheral heat insulating means including at least onemovable heat shield on one side of said working zone; and

(e) means mounting said movable heat shield on said upper platenassembly for movement relative thereto between an operative positionwherein it blocks heat loss from said working zone, and an inoperativeposition wherein it provides for access to said working zone from saidone side thereof.

2. A hot press according to claim 1 wherein said peripheral heatinsulating means includes another movable heat shield on the oppositeside of said working zone from the first movable heat shield mentioned,said hot press including another mounting means mounting said othermovable heat shield on said upper platen assembly for movement relativethereto between an operative position wherein it blocks heat loss fromsaid opposite side of said working zone and an inoperative positionwherein it provides for access to said working zone from said oppositeside thereof.

3. A hot press as set forth in claim 2 wherein said mounting meansrespectively mount said movable heat shields for movement between theiroperative and inoperative positions in directions generallyperpendicular to said platens.

4. A hot press as defined in claim 3 wherein each of said mounting meansincludes a pivotable shaft carried by said upper platen assembly andparallel to the corresponding side of said working zone and having armspivotally connected to an upper edge of the corresponding one of saidheat shields.

5. A hot press as set forth in claim 4 including actuating meansconnected to each of said shafts for pivoting same to move thecorresponding one of said heat shields between its operative andinoperative positions.

6. A hot press according to claim 1 including two refractory layersrespectively positioned adjacent the surfaces of said platens oppositethe surfaces thereof which bound said working zone.

7. A hot press as defined in claim 6 including platenedge heatinsulating means respectively extending along the edges of said platensfor minimizing heat losses from said platen edges.

8. In a platen assembly for a hot press, or the like, the combinationof:

(a) a platen having a working surface;

(b) means for heating said platen;

(c) a refractory layer adjacent and engaging the surface of said platenopposite said working surface thereof and comprising a plurality ofseparate refractory blocks; and

(d) means permitting a relative expansion and contraction of said platenand said refractory layer, in directions parallel to said workingsurface, for connecting said platen and said refractory layer together.

9. A platen assembly according to claim 8 wherein said connecting meansincludes a plurality of bolts extending through said platen and saidrefractory layer and disposed in openings in one of them at least someof which are laterally enlarged.

10. A platen assembly as defined in claim 9 wherein said laterallyenlarged openings are laterally enlarged substantially along linesradiating from the center of said platen.

11. A platen assembly according to claim 10 wherein said laterallyenlarged openings are formed in said platen.

12. A platen assembly according to claim 11 including means comprisingcompression springs encircling said bolts for yieldably biasing saidplaten and said refractory layer together.

13. In a hot press, the combination of:

(a) upper and lower platen assembly respectively including upper andlower platens, said upper platen assembly being movable upwardly anddownwardly away from and toward said lower platen assembly;

(b) said lower platen assembly being movable horizontally relative tosaid upper platen assembly between a retracted, operative position inregister with said upper platen assembly and an extended, inoperativeposition out of register therewith;

(c) horizontally opposed clamping means carried by said lower platenassembly on opposite side thereof;

(d) actuating means for said clamping means respectively connectedthereto;

(e) one of said actuating means being in register with said upper platenassembly when said lower platen assembly is in its extended position;

(f) means for heating at least one of said platens to provide a heatedworking zone therebetween when sail lower platen assembly is in itsretracted position; an

(g) heat insulating means carried by said lower platen assembly forprotecting said one actuating means from heat from said upper platenwhen said lower platen assembly is in its extended position.

References Cited UNITED STATES PATENTS 2,944,500 7/1960 Raynes 72-3423,015,292 1/1962 Bridwell 72342 3,025,905 3/1962 Haerr 72342 3,350,91311/1967 Bergholdt, et al. 72-342 CHARLES W. LANHAM, Primary ExaminerLOWELL A. LARSON, Assistant Examiner

